BIOL 366 Lecture Notes - Lecture 15: Pronucleus, Blastoderm, Syncytium
Document Summary
Record holding d. bifurca and cryptic selection. Sperm is so long it wraps around the oocyte. Structures that are this big have an evolutionary cost. Drosophila is easy to breed, hardy, prolific, and tolerant to diverse conditions, and they have polytene chromosomes (dna replicates several times without separating) Cell membrane does not form until 13th division. Axial differences are generated by the position of the egg within the (cid:373)other"s egg (cid:272)ha(cid:373)(cid:271)er. Pole cells begin at cycle 9 - have their own developmental fate stage 13 - cellular blastoderm - see our first cells. Fertilization sperm enters an egg that is already activated. Egg activation is accomplished at ovulation, before fertilization there is only one site where the sperm can enter the egg. This is the micropyle, a tunnel in the chorion (eggshell) located at the future dorsal anterior region of the embryo. Allows sperm to pass through it one at a time and prevents polyspermy.
